SCATOPUAGA LUTARIA AND 5. STERCORARIA. 413 



* 



complicated piece of mechanism (Fig. 8). Behind the penis 

 is a curious club-shaped hook (Fig. 9), which varies exceedingly 

 in shape in the different species. 



The terminology given above can be apphed to the outer plates, 

 which appear to coriespond with the forcipes inferiores, while the 

 outer claspers are the forcipes superiores. The palpi and inner 

 claspers are only appendages of the appendix interna or admini- 

 culum. The other parts — the laminae hasales and laminae 

 superiores — are difficult to identify. 



To find a corresponding part to the club-shaped hook we must 

 turn to Blatta, where there is a similar process in apposition to 

 the penis ; in this insect it is called the *' titillator."* 



The organs in Scatophaga are shown diagrammatically in 

 Fig. 1, and a lateral view, with the outer plates and claspers 

 removed, is given in Fig. 8. The hook (Fig. 9) is posterior to the 

 penis. On the anterior edge of the cavity of the hypopygium 

 are the two spiny processes shown in Fig. 1. They perhaps may 

 be homologues of the laminae superiores. 



The spermatozoa are contained in two chitinous sacs, provided 

 with an intricate ramification of nerves, and leading by two long 

 tubes {vasa deferentia) to the ejaculatory organ. 



These parts are those found in S. lutaria. The general plan of 

 those belonging to S. stercoi'aria is similar, but varies in detail. 

 The larger hooks (Fig. 4) differ in shape, the palpi (Fig. 5) are 

 shorter and more bristly, and the inner hooks (Fig. 2) have 

 rounded blunt ends. The penis is shaped differently, and is 

 shown (Fig. 6) drawn to about the same scale as Figs. 2, 3, 4, 

 and 5. The shapes of the two organs are very dissimilar. 

 *S'. stercoraria has two minute hooks on the upper part of the 

 penis, and the accompanying posterior hook is fused at the base 

 and exceedingly modified in shape. The most striking variation 

 is the presence of an organ of spatulated shape, which I have 

 failed to find in >S'. lutaria (Fig. 7). This part has much the 

 same appearance in Lucilla cornicina and Palloptera ustulata, 

 but in Nemopoda cylindrica it is much elongated. It appears 

 to be a lever or apodeme, to which powerful muscles are 

 attached. 



Professor A. Berlese t has studied the copulation of the house-fly 



* " The Cockroach," Miall & Denny. 



t " Riv. Patol. Vegetale," ix. (1902), pp. 345-56. 



